1. Field of the Invention
The present invention relates to the field of electrophotographic copying, and more particularly, to a method of electrophotographic copying whereby multiple copies can be formed from the same electrostatic image.
2. Description of the Prior Art
In customary electrophotographic processes, a conductive backing having a photoconductive insulating layer thereon is electrostatically imaged by first uniformly charging its surface, and subsequently exposing the charged surface to a pattern of activating electromagnetic radiation, such as light. The radiation pattern selectively dissipates electrostatic charges in the illuminated area on the photoconductive surface, which results in formation of a latent electrostatic image in non-illuminated areas. This latent electrostatic image can be developed to form a visible image by depositing developer materials thereon by a variety of development techniques, the most common of which is cascade development.
Typically, each latent electrostatic image is developed only once, thus producing one electrophotographic copy for each charging/exposure cycle. While not commonly practiced, methods have been proposed in which multiple electrophotographic copies are formed from each latent electrostatic image. Typically, such processes involve repeatedly cycling an electrostatic image through the development and transfer steps. See, for example, Kaupp U.S. Pat. No. 3,685,896. Such techniques have not generally been commercially accepted, however, because of certain problems inherent therein, and one such problem relates to loss of image density on copies beyond the first.